1. Field of the Invention
This invention relates to an adhesive for lamination which is good in adhesiveness to all substrates such as plastic films, metal foils, metallized films, paper and the like.
2. Related Prior Art
As an adhesive for laminating various plastic films, metal foils, metallized films, paper and the like, there have been used synthetic resins such as polyurethane resin, vinyl acetate resin, acrylic resin, polyamide resin, epoxy resin and the like; natural resins such as hide glue, casein, gelatine, starch, cellulose and the like; etc. Among them, adhesives for lamination in which a synthetic resin is used are the main current in respects of easiness of molecular design, high productivity and the like, and particularly those in which polyurethane resin is used have been widely employed from the viewpoint of excellent bonding performance, durability, heat resistance and the like, from the viewpoint of broad range of applicability to various films, and the like.
One of the properties required for adhesives is that the adhesives indicate good wettability to film substrates. The adhesive-coating step in a process for producing a laminate film is generally to coat an adhesive on a film while the film is moved at a high speed. Accordingly, the xe2x80x9cwettabilityxe2x80x9d required for adhesives for lamination includes not only the conventional xe2x80x9cstatic wettabilityxe2x80x9d but also the xe2x80x9cdynamic wettabilityxe2x80x9d to a film which is moving at a high speed. As to the adhesives for lamination which have been known by now, such a viewpoint has been lacking, and hence, troubles have often been caused such as bad appearance of laminate film, lack of bonding strength due to bad coating of adhesive, and the like.
In addition, the laminate film is produced in many cases by laminating two films having different properties to each other, for example, laminating an aluminum foil to a polyethylene film, a polyethylene terephthalate film to a polypropylene film, or the like, depending upon the required properties such as gas barrier property, heat-sealing property and the like. However, there have been known no appropriate adhesives which have good wettability to both of such diverse films as in bonding a polyethylene film to a polyethylene terephthalate film, bonding a polypropylene film to a nylon film, bonding a polyethylene terephthalate film to an aluminum foil, and the like.
The present inventors have made diligent examination for solving such problems, and have consequently found that the above-mentioned problems can be solved by adhesives for lamination in which a resin having a wettability of at least the specified value with regard to various films is used, whereby this invention has been accomplished.
An object of this invention is to provide an adhesive for lamination comprising a resin having a specific dynamic wettability.
Another object of this invention is to provide an adhesive for lamination which comprises a resin having a specific dynamic wettability and a polyisocyanate curing agent.
Other objects and advantages of this invention will become apparent from the following description.
According to this invention, there is provided an adhesive for lamination which comprises a resin whose dynamic wettability to a film substrate is at least 0.20 mN.
According to this invention, there is further provided an adhesive for lamination which comprises a resin whose dynamic wettability to a film substrate is at least 0.20 mN and a polyisocyanate curing agent.